ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Fri, 17 Jan 2020 16:02:00 GMT2020-01-17T16:02:00Z50251- A new AF gravitational instantonhttps://scholarbank.nus.edu.sg/handle/10635/95648Title: A new AF gravitational instanton
Authors: Chen, Y.; Teo, E.
Abstract: It has long been conjectured that the Euclidean Schwarzschild and Euclidean Kerr instantons are the only non-trivial asymptotically flat (AF) gravitational instantons. In this Letter, we show that this conjecture is false by explicitly constructing a new two-parameter AF gravitational instanton with a U(1)×U(1) isometry group, using the inverse-scattering method. It has Euler number χ=3 and Hirzebruch signature τ=1, and its global topology is CP2 with a circle S1 removed appropriately. Various other properties of this gravitational instanton are also discussed. © 2011 Elsevier B.V.
Wed, 14 Sep 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/956482011-09-14T00:00:00Z
- A no-go theorem for accelerating cosmologies from M-theory compactificationshttps://scholarbank.nus.edu.sg/handle/10635/95654Title: A no-go theorem for accelerating cosmologies from M-theory compactifications
Authors: Teo, E.
Abstract: It is known that four-dimensional cosmologies exhibiting transient phases of acceleration can be obtained by compactifications of low-energy effective string or M-theory on time-varying manifolds. In the four-dimensional theory, the acceleration can be attributed to a quintessential scalar field with a positive effective potential. Recently, Townsend has conjectured that the potentials obtained by such compactifications cannot give rise to late-time accelerating universes which possess future event horizons. Such a 'no-go' result would be desirable, since current string or M-theory seems unable to provide an adequate description of space-times with future event horizons. In this Letter, we provide a proof of this conjecture for a class of warped compactifications with a single scalar modulus parametrising the volume of the compactification manifold. © 2005 Elsevier B.V. All rights reserved.
Thu, 10 Mar 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/956542005-03-10T00:00:00Z
- Black diholes in five dimensionshttps://scholarbank.nus.edu.sg/handle/10635/95873Title: Black diholes in five dimensions
Authors: Teo, E.
Abstract: Using a generalized Weyl formalism, we show how stationary, axisymmetric solutions of the four-dimensional vacuum Einstein equation can be turned into static, axisymmetric solutions of five-dimensional dilaton gravity coupled to a two-form gauge field. This procedure is then used to obtain new solutions of the latter theory describing pairs of extremal magnetic black holes with opposite charges, known as black diholes. These diholes are kept in static equilibrium by membranelike conical singularities stretching along two different directions. We also present solutions describing diholes suspended in a background magnetic field, and with unbalanced charges. © 2003 The American Physical Society.
Wed, 01 Jan 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/958732003-01-01T00:00:00Z
- Rod-structure classification of gravitational instantons with U(1)×U(1) isometryhttps://scholarbank.nus.edu.sg/handle/10635/97832Title: Rod-structure classification of gravitational instantons with U(1)×U(1) isometry
Authors: Chen, Y.; Teo, E.
Abstract: The rod-structure formalism has played an important role in the study of black holes in D=4 and 5 dimensions with R×U(1)D-3 isometry. In this paper, we apply this formalism to the study of four-dimensional gravitational instantons with U(1)×U(1) isometry, which could serve as spatial backgrounds for five-dimensional black holes. We first introduce a stronger version of the rod structure with the rod directions appropriately normalised, and show how the regularity conditions can be read off from it. Requiring the absence of conical and orbifold singularities will in general impose periodicity conditions on the coordinates, and we illustrate this by considering known gravitational instantons in this class. Some previous results regarding certain gravitational instantons are clarified in the process. Finally, we show how the rod-structure formalism is able to provide a classification of gravitational instantons, and speculate on the existence of possible new gravitational instantons. © 2010 Elsevier B.V.
Fri, 01 Oct 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/978322010-10-01T00:00:00Z
- A new form of the rotating C-metrichttps://scholarbank.nus.edu.sg/handle/10635/95651Title: A new form of the rotating C-metric
Authors: Hong, K.; Teo, E.
Abstract: In a previous paper, we showed that the traditional form of the charged C-metric can be transformed, by a change of coordinates, into one with an explicitly factorizable structure function. This new form of the C-metric has the advantage that its properties become much simpler to analyse. In this paper, we propose an analogous new form for the rotating charged C-metric, with structure function G(ξ) = (1 - ξ 2)(1 + r+Aξ)(1 + r_Aξ), where r ± are the usual locations of the horizons in the Kerr-Newman black hole. Unlike the non-rotating case, this new form is not related to the traditional one by a coordinate transformation. We show that the physical distinction between these two forms of the rotating C-metric lies in the nature of the conical singularities causing the black holes to accelerate apart: the new form is free of torsion singularities and therefore does not contain any closed timelike curves. We claim that this new form should be considered the natural generalization of the C-metric with rotation.
Fri, 07 Jan 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/956512005-01-07T00:00:00Z
- A doubly rotating black ring with dipole chargehttps://scholarbank.nus.edu.sg/handle/10635/95619Title: A doubly rotating black ring with dipole charge
Authors: Chen, Y.; Hong, K.; Teo, E.
Abstract: We present a dipole-charged generalisation of the Pomeransky-Sen'kov black ring in five-dimensional Kaluza-Klein theory. It rotates in two independent directions, although one of the rotations has been tuned to achieve balance, so that the space-time does not contain any conical singularities. This solution was constructed using the inversescattering method in six-dimensional vacuum gravity. We then study various physical properties of this solution, with particular emphasis on the new features that the dipole charge introduces. © 2012 SISSA.
Sun, 01 Jan 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/956192012-01-01T00:00:00Z
- Rotating black rings on Taub-NUThttps://scholarbank.nus.edu.sg/handle/10635/97848Title: Rotating black rings on Taub-NUT
Authors: Chen, Y.; Teo, E.
Abstract: In this paper, we construct new solutions describing rotating black rings on Taub-NUT using the inverse-scattering method. These are five-dimensional vacuum spacetimes, generalising the Emparan-Reall and extremal Pomeransky-Sen'kov black rings to a Taub-NUT background space. When reduced to four dimensions in Kaluza-Klein theory, these solutions describe (possibly rotating) electrically charged black holes in superposition with a finitely separated magnetic monopole. Various properties of these solutions are studied, from both a five- and four-dimensional perspective. © SISSA 2012.
Sun, 01 Jan 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/978482012-01-01T00:00:00Z
- Black holes on gravitational instantonshttps://scholarbank.nus.edu.sg/handle/10635/95876Title: Black holes on gravitational instantons
Authors: Chen, Y.; Teo, E.
Abstract: In this paper, we classify and construct five-dimensional black holes on gravitational instantons in vacuum Einstein gravity, with R×U(1)×U(1) isometry. These black holes have spatial backgrounds which are Ricci-flat gravitational instantons with U(1)×U(1) isometry, and are completely regular space-times outside the event horizon. Most of the known exact five-dimensional vacuum black-hole solutions can be classified within this scheme. Amongst the new space-times presented are static black holes on the Euclidean Kerr and Taub-bolt instantons. We also present a rotating black hole on the Eguchi-Hanson instanton. © 2011 Elsevier B.V.
Sun, 11 Sep 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/958762011-09-11T00:00:00Z
- New form of the C metric with cosmological constanthttps://scholarbank.nus.edu.sg/handle/10635/128001Title: New form of the C metric with cosmological constant
Authors: Chen Y.; Lim Y.-K.; Teo E.
Thu, 01 Jan 2015 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1280012015-01-01T00:00:00Z
- Spherical Photon Orbits around a Kerr Black Holehttps://scholarbank.nus.edu.sg/handle/10635/97985Title: Spherical Photon Orbits around a Kerr Black Hole
Authors: Teo, E.
Abstract: Two circular photon orbits are known to exist in the equatorial plane of the Kerr black hole. In this paper, we investigate so-called spherical photon orbits-orbits with constant coordinate radii that are not confined to the equatorial plane. A one-parameter class of solutions is found, which includes the circular orbits as special cases. The properties of these spherical orbits are then analyzed, with the aim of classifying them by qualitative differences in their behavior. Finally, representative orbits from each class are plotted out, including a zero-angular momentum photon orbit and one with non-fixed azimuthal direction.
Sat, 01 Nov 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/979852003-11-01T00:00:00Z
- A new form of the C-metrichttps://scholarbank.nus.edu.sg/handle/10635/95650Title: A new form of the C-metric
Authors: Hong, K.; Teo, E.
Abstract: The usual form of the C-metric has the structure function G(ξ) = 1 - ξ2 - 2m Aξ3, whose cubic nature can make calculations cumbersome, especially when explicit expressions for its roots are required. In this paper, we propose a new form of the C-metric, with the explicitly factorizable structure function G(ξ) = (1 - ξ2)(1 + 2m Aξ). Although this form is related to the usual one by a coordinate transformation, it has the advantage that its roots are now trivial to write down. We show that this leads to potential simplifications, for example, when casting the C-metric in Weyl coordinates. These results also extend to the charged C-metric, whose structure function can be written in a new form G(ξ) = (1 - ξ2)(1 + r+Aξ)(1 + r-Aξ), where r± are the usual locations of the horizons in the Reissner-Nordström solution. As a by-product, we explicitly cast the extremally charged C-metric in Weyl coordinates.
Mon, 21 Jul 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/956502003-07-21T00:00:00Z
- Rotating black lens solution in five dimensionshttps://scholarbank.nus.edu.sg/handle/10635/97847Title: Rotating black lens solution in five dimensions
Authors: Chen, Y.; Teo, E.
Abstract: It has recently been shown that a stationary, asymptotically flat vacuum black hole in five space-time dimensions with two commuting axial symmetries must have an event horizon with either a spherical, ring or lens-space topology. In this paper, we study the third possibility, a so-called black lens with L(n,1) horizon topology. Using the inverse scattering method, we construct a black-lens solution with the simplest possible rod structure, and possessing a single asymptotic angular momentum. Its properties are then analyzed; in particular, it is shown that there must either be a conical singularity or a naked curvature singularity present in the space-time. © 2008 The American Physical Society.
Tue, 23 Sep 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/978472008-09-23T00:00:00Z
- Quantum interest in two dimensionshttps://scholarbank.nus.edu.sg/handle/10635/97687Title: Quantum interest in two dimensions
Authors: Teo, E.; Wong, K.F.
Abstract: The quantum interest conjecture of Ford and Roman asserts that any negative-energy pulse must necessarily be followed by an overcompensating positive-energy one within a certain maximum time delay. Furthermore, the minimum amount of over-compensation increases with the separation between the pulses. In this paper we first study the case of a negative-energy square pulse followed by a positive-energy one for a minimally coupled, massless scalar field in two-dimensional Minkowski space. We obtain explicit expressions for the maximum time delay and the amount of over-compensation needed, using a previously developed eigenvalue approach. These results are then used to give a proof of the quantum interest conjecture for massless scalar fields in two dimensions, valid for general energy distributions. © 2002 The American Physical Society.
Tue, 01 Jan 2002 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/976872002-01-01T00:00:00Z
- Black diholes with unbalanced magnetic chargeshttps://scholarbank.nus.edu.sg/handle/10635/95874Title: Black diholes with unbalanced magnetic charges
Authors: Liang, Y.C.; Teo, E.
Abstract: We present a technique that can be used to generate a static, axisymmetric solution of the Einstein-Maxwelldilaton equations from a stationary, axisymmetric solution of the vacuum Einstein equations. Starting from the Kerr solution, Davidson and Gedalin have previously made use of this technique to obtain a pair of oppositely charged, extremal dilatonic black holes, known as a black dihole. In this paper, we shall instead start from the Kerr-NUT (Newman-Unti-Tamburino) solution. It will be shown that the new solution can also be interpreted as a dihole, but with the black holes carrying unbalanced magnetic charges. The effect of the NUT parameter is to introduce a net magnetic charge into the system. Finally, we uplift our solution to ten dimensions to describe a system consisting of D6 and anti-D6-branes with unbalanced charges. The limit in which they coincide agrees with a solution recently derived by Brax et al. ©2001 The American Physical Society.
Mon, 01 Jan 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/958742001-01-01T00:00:00Z
- Balanced electric-magnetic dihole in Kaluza-Klein theoryhttps://scholarbank.nus.edu.sg/handle/10635/95842Title: Balanced electric-magnetic dihole in Kaluza-Klein theory
Authors: Chen, Y.; Teo, E.
Abstract: We present a four-dimensional double-black-hole (or dihole) solution in Kaluza-Klein theory, describing a superposition of an electrically charged and a magnetically charged black hole. This system can be balanced for appropriately chosen parameters, and the resulting space-time is completely regular on and outside the event horizons. This solution was constructed using the inverse-scattering method in five-dimensional vacuum gravity, in which it describes a rotating black ring surrounding a static black hole on a Taub-NUT background space. Various properties of this solution are studied, from both a four- and five-dimensional perspective. © SISSA 2012.
Sun, 01 Jan 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/958422012-01-01T00:00:00Z
- Accelerating black diholes and static black diringshttps://scholarbank.nus.edu.sg/handle/10635/95719Title: Accelerating black diholes and static black dirings
Authors: Teo, E.
Abstract: We show how a recently discovered black-ring solution with a rotating 2-sphere can be turned into two new solutions of Einstein-Maxwell-dilaton theory. The first is a four-dimensional solution describing a pair of oppositely charged, extremal black holes-known as a black dihole-undergoing uniform acceleration. The second is a five-dimensional solution describing a pair of concentric, static extremal black rings carrying opposite dipole charges-a so-called black diring. The properties of both solutions, which turn out to be formally very similar, are analyzed in detail. We also present, in an appendix, an accelerating version of the Zipoy-Voorhees solution in four-dimensional Einstein gravity. © 2006 The American Physical Society.
Sun, 15 Jan 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/957192006-01-15T00:00:00Z
- Generalized planar black holes and the holography of hydrodynamic shearhttps://scholarbank.nus.edu.sg/handle/10635/96706Title: Generalized planar black holes and the holography of hydrodynamic shear
Authors: McInnes, B.; Teo, E.
Abstract: AdS black holes with planar event horizon topology play a central role in AdS/CFT holography, and particularly in its applications. Generalizations of the known planar black holes can be found by considering the Plebański-Demiański metrics, a very general family of exactly specified solutions of the Einstein equations. These generalized planar black holes may be useful in applications. We give a concrete example of this in the context of the holographic description of the Quark-Gluon Plasma (QGP). We argue that our generalized planar black holes allow us to construct a model of the internal shearing motion generated when the QGP is produced in peripheral heavy-ion collisions. When embedded in string theory, the bulk physics is in fact unstable. We find however that this instability may develop too slowly to affect the evolution of the plasma, except possibly for high values of the quark chemical potential, such as will be studied in experimental scans of the quark matter phase diagram. © 2013 The Authors.
Wed, 01 Jan 2014 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/967062014-01-01T00:00:00Z
- Multi-black-hole solutions in five dimensionshttps://scholarbank.nus.edu.sg/handle/10635/97266Title: Multi-black-hole solutions in five dimensions
Authors: Tan, H.S.; Teo, E.
Abstract: Using a recently developed generalized Weyl formalism, we construct an asymptotically flat, static vacuum Einstein solution that describes a superposition of multiple five-dimensional Schwarzschild black holes. The spacetime exhibits a U(1) × U(1) rotational symmetry. It is argued that for certain choices of parameters the black holes are collinear and so may be regarded as a five-dimensional generalization of the Israel-Khan solution. The black holes are kept in equilibrium by membranelike conical singularities along the two rotational axes; however, they still distort one another by their mutual gravitational attraction. We also generalize this solution to one describing multiple charged black holes, with fixed mass-to-charge ratio, in Einstein-Max well-dilaton theory. æ 2003 The American Physical Society.
Wed, 01 Jan 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/972662003-01-01T00:00:00Z
- Monopoles, vortices, and kinks in the framework of noncommutative geometryhttps://scholarbank.nus.edu.sg/handle/10635/97256Title: Monopoles, vortices, and kinks in the framework of noncommutative geometry
Authors: Teo, E.; Ting, C.
Abstract: Noncommutative differential geometry allows a scalar field to be regarded as a gauge connection, albeit on a discrete space. We explain how the underlying gauge principle corresponds to the independence of physics on the choice of vacuum state, should it be nonunique. A consequence is that Yang-Mills-Higgs theory can be reformulated as a generalized Yang-Mills gauge theory on Euclidean space with a Z2 internal structure. By extending the Hodge star operation to this noncommutative space, we are able to define the notion of self-duality of the gauge curvature form in arbitrary dimensions. It turns out that BPS monopoles, critically coupled vortices, and kinks are all self-dual solutions in their respective dimensions. We then prove, within this unified formalism, that static soliton solutions to the Yang-Mills-Higgs system exist only in one, two, and three spatial dimensions.
Fri, 15 Aug 1997 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/972561997-08-15T00:00:00Z
- Unbalanced Pomeransky-Sen'kov black ringhttps://scholarbank.nus.edu.sg/handle/10635/98510Title: Unbalanced Pomeransky-Sen'kov black ring
Authors: Chen, Y.; Hong, K.; Teo, E.
Abstract: The Pomeransky-Sen'kov solution is well known to describe an asymptotically flat doubly rotating black ring in five dimensions, whose self-gravity is exactly balanced by the centrifugal force arising from the rotation in the ring direction. In this paper, we generalize this solution to the unbalanced case, in which there is in general a conical singularity in the space-time. Unlike a previous form of this solution presented in the literature, our form is much more compact. We describe in detail how this solution can be derived using the inverse-scattering method, and study its various properties. In particular, we show how various known limits can be recovered as special cases of this solution. © 2011 American Physical Society.
Mon, 17 Oct 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/985102011-10-17T00:00:00Z
- Statistical entropy of charged two-dimensional black holeshttps://scholarbank.nus.edu.sg/handle/10635/98018Title: Statistical entropy of charged two-dimensional black holes
Authors: Teo, E.
Abstract: The statistical entropy of a five-dimensional black hole in Type II string theory was recently derived by showing that it is U-dual to the three-dimensional Bañados-Teitelboim-Zanelli black hole, and using Carlip's method to count the microstates of the latter. This is valid even for the non-extremal case, unlike the derivation which relies on D-brane techniques. In this letter, I shall exploit the U-duality that exists between the five-dimensional black hole and the two-dimensional charged black hole of McGuigan, Nappi and Yost, to microscopically compute the entropy of the latter. It is shown that this result agrees with previous calculations using thermodynamic arguments. © 1998 Elsevier Science B.V. All rights reserved.
Thu, 25 Jun 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/980181998-06-25T00:00:00Z
- Bounds on negative energy densities in static space-timeshttps://scholarbank.nus.edu.sg/handle/10635/95887Title: Bounds on negative energy densities in static space-times
Authors: Fewster, C.J.; Teo, E.
Abstract: Certain exotic phenomena in general relativity, such as backward time travel, appear to require the presence of matter with negative energy. While quantum fields are a possible source of negative energy densities, there are lower bounds-known as quantum inequalities - that constrain their duration and magnitude. In this paper, we derive new quantum inequalities for scalar fields in static space-times, as measured by static observers with a choice of sampling function. Unlike those previously derived by Pfenning and Ford, our results do not assume any specific sampling function. We then calculate these bounds in static three- and four-dimensional Robertson-Walker universes, the de Sitter universe, and the Schwarzschild black hole. In each case, the new inequality is stronger than that of Pfenning and Ford for their particular choice of sampling function. ©1999 The American Physical Society.
Sat, 15 May 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/958871999-05-15T00:00:00Z
- Black hole absorption cross-sections and the anti-de Sitter-conformal field theory correspondencehttps://scholarbank.nus.edu.sg/handle/10635/95875Title: Black hole absorption cross-sections and the anti-de Sitter-conformal field theory correspondence
Authors: Teo, E.
Abstract: Recent work has uncovered a correspondence between theories in anti-de Sitter space, and those on its boundary. This has important implications for black holes in string theory which have near-horizon AdS geometries. Using the effective coupling to the boundary conformal field theory, I compute the low-energy, s-wave absorption cross-sections for a minimally coupled scalar in the near-extremal four- and five-dimensional black holes. The results agree precisely with semi-classical gravity calculations. Agreement for fixed scalars, and for the BTZ black hole, is also found. © 1998 Elsevier Science B.V. All rights reserved.
Thu, 24 Sep 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/958751998-09-24T00:00:00Z
- Quantum inequalities and "quantum interest" as eigenvalue problemshttps://scholarbank.nus.edu.sg/handle/10635/97685Title: Quantum inequalities and "quantum interest" as eigenvalue problems
Authors: Fewster, C.J.; Teo, E.
Abstract: Quantum inequalities (QI's) provide lower bounds on the averaged energy density of a quantum field. We show how the QI's for massless scalar fields in even dimensional Minkowski space may be reformulated in terms of the positivity of a certain self-adjoint operator - a generalized Schrödinger operator with the energy density as the potential - and hence as an eigenvalue problem. We use this idea to verify that the energy density produced by a moving mirror in two dimensions is compatible with the QI's for a large class of mirror trajectories. In addition, we apply this viewpoint to the "quantum interest conjecture"of Ford and Roman, which asserts that the positive part of an energy density always overcompensates for any negative components. For various simple models in two and four dimensions we obtain the best possible bounds on the "quantum interest rate" and on the maximum delay between a negative pulse and a compensating positive pulse. Perhaps surprisingly, we find that - in four dimensions - it is impossible for a positive δ-function pulse of any magnitude to compensate for a negative δ-function pulse, no matter how close together they occur. ©2000 The American Physical Society.
Sat, 15 Apr 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/976852000-04-15T00:00:00Z
- Rotating traversable wormholeshttps://scholarbank.nus.edu.sg/handle/10635/97849Title: Rotating traversable wormholes
Authors: Teo, E.
Abstract: The general form of a stationary, axially symmetric traversable wormhole is discussed. This provides an explicit class of rotating wormholes that generalizes the static, spherically symmetric ones first considered by Morris and Thorne. In agreement with general analyses, it is verified that such a wormhole generically violates the null energy condition at the throat. However, for suitable model wormholes, there can be classes of geodesics falling through it which do not encounter any energy-condition-violating matter. The possible presence of an ergoregion surrounding the throat is also noted.
Wed, 15 Jul 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/978491998-07-15T00:00:00Z